A quantized lattice vibration in a crystal is called a phonon, and various physical phenomena generated in a crystal, including specific heat, can be correctly described by introducing the idea of the phonon. Although the phonon can be understood as a form of thermal vibration energy of a crystal lattice, an elastic wave (acoustical wave) propagating in a crystal is also another form of the phonon with an extremely low vibration frequency.
Conventionally, piezoelectric resonators such as a quartz oscillator and a surface acoustic wave device are widely used as electric parts using an acoustical wave in a crystal. However, integration of those piezoelectric resonators with other semiconductor electron circuitry has been difficult.
Meanwhile, there has been known a method of realizing the phonon oscillator, using an interaction between electrons and the phonons inside a semiconductor crystal. However, in the conventional method, it is difficult to realize such a phonon oscillator with the use of an integrated circuit process.